Problem Description: An element with a value of 0 in a two-dimensional array, where the row or column is full set is 0;https://leetcode.com/problems/set-matrix-zeroes/
Problem Analysis: Constant space is required in the question. Naturally think of bit optimization. An int can store information for 31 elements. Here is the use of the string in the paper is commonly used in the optimization of processing methods. Like the idea of a barrel. Well, it seems that this long paper is not a white look.
Attached code:
1 voidSetzeroes (vector<vector<int>>&matrix) {2 intn = matrix.size (), M = matrix[0].size ();3 int*row = (int*)malloc(N/ to+2) *sizeof(int));4 int*col = (int*)malloc((M/ to+2) *sizeof(int));5 7 for(inti =0; I < n/ to+2; i + +) row[i] =0;8 for(inti =0; I < m/ to+2; i + +) col[i] =0;9 Ten intPosint, Posbit; One for(inti =0; I < n; i + +){ A for(intj =0; J < M; J + +){ - if(Matrix[i][j] = =0){ -cout<<"i ="<<i <<"j ="<<j <<Endl; thePosint = I/ to, posbit = i% to; -Row[posint] |= (1<<posbit); -Posint = J/ to, Posbit = j to; -Col[posint] |= (1<<posbit); + } - } + } A at for(inti =0; I < n; i + +){ -Posint = I/ to;p osbit = i% to; - if(Row[posint] & (1<<posbit)) { - for(intj =0; J < M; J + +){ -MATRIX[I][J] =0; - } in } - } to + for(inti =0; I < m; i + +){ -Posint = I/ to;p osbit = i% to; the if(Col[posint] & (1<<posbit)) { * for(intj =0; J < N; J + +){ $Matrix[j][i] =0;Panax Notoginseng } - } the } +}
Reflection: Originally a very simple question medium difficulty, but encountered a big pit, that is, I began to use the Memset function to initialize the dynamic array row and Col. Big data on the strange bug, and finally found a long time to locate this initialization function here, using the For loop manual initialization, the problem is resolved.
Memset is used to initialize a string, but since ASCII (0) = Null,null is exactly 0, it can be used to initialize the array to 0, but it is important to note that the size of the initialization (n * sizeof int) is not initialized char[]. The direct use of sizeof (array name) confusion, here *row is just a pointer to the N-int region, the size of an int is also.
"Leetcode"--73. Set Matrix Zeroes